1. Field of the Invention
The present invention relates to a light guide apparatus, a backlight apparatus and a liquid crystal display (LCD) apparatus using the backlight apparatus.
2. Description of the Related Art
A backlight apparatus has been used as a light source of an LCD apparatus. FIG. 1(A) shows an LCD apparatus using a conventional backlight apparatus. The conventional backlight apparatus includes a fluorescent lamp 1 generating white light, a reflecting cover 2 mounted to surround a top side, a bottom side and a rear side of the fluorescent lamp 1, a wedge-type light guide 3, a light scattering layer 4 attached on the bottom surface of the light guide 3, a metallic reflector 5 placed below the light guide 3, and light-shaping films 6 and 7 placed above the light guide 3. A prism sheet, which refracts the incidence light directed from an oblique direction toward a vertical direction of the prism sheet, is frequently used as the light-shaping films 6 and 7. The light scattering layer 4 is actually a dotted pattern printed on the bottom surface of the light guide 3.
Each of the dots diffuses the incidence light upwardly with a large angle distribution, as shown in a right side portion of the light scattering layer 4 in FIG. 1. By controlling the density of the dots over the bottom surface of the light guide 3, the backlight apparatus can uniformly pass the light through from the top surface of the light guide 3. The emitted light from the top surface of the light guide 3 is diffused with a large angle distribution. For some applications such as an LCD apparatus for notebook personal computers, this angle distribution of the emitted light is so large that the efficiency of usage of the light from the light source, or the fluorescent lamp 1 is not high. Therefore, one or more light-shaping sheets are used to obtain the appropriate angle distribution. The metallic reflector 5 serves as a light recirculator, which can reflect the light leaking out from the bottom light scattering layer 4 back into the light guide 3, for light recycling.
The light emitted by the backlight apparatus is directed to an LCD panel 10 through a polarizer 8. A polarizer 9 also is placed above the LCD panel 10. The LCD panel 10 includes an upper glass substrate 11 and a lower glass substrate 12, and peripheral edges of both the glass substrates 11 and 12 are sealed by a sealing area 13. A color filter which includes red, green and blue color filter segments, and a common electrode, not shown in FIG. 1(A), are formed on the inner surface of the upper glass substrate 11 to realize the color LCD apparatus. One pixel is constituted by three sub-pixels (i.e., the R, G and B sub-pixels). The liquid crystal material, such as a 90-degrees twisted nematic (TN) liquid crystal material is enclosed within the space between the glass substrates 11 and 12.
A first problem of the conventional backlight apparatus is that it is very difficult to obtain the light emitted with an angle spread less than 10 degrees FWHM (Full Width at Half Maximum), as shown in FIG. 1(B).
Another problem of the conventional backlight apparatus is that the backlight apparatus requires many components, some of which are not easily fabricated, so that the fabrication cost becomes high.
A third problem of the conventional backlight apparatus is that since the light from the fluoresecent lamp 1 passes through many components, the intensity of the light is largely attenuated while passing through the components.